<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            width: 600px;
            height: 200px;
            border: 1px solid #ccc;

            /* 尺寸调节 */
            overflow: auto;
            resize: both;

            /* 盒子阴影 */
            box-shadow: 10px 10px 5px 2px #ccc;
        }
        .container div{
            width: 200px;
            height: 200px;
            border: 1px solid red;
            float: left;
            padding: 5px;

            /* 盒子此时的width和height，是包含border、padding */
            box-sizing: border-box;

            /* margin-left: 5px; */
        }
    </style>
</head>
<body>
    <div class="container">
        <div>div1</div>
        <div>div2</div>
        <div>div3</div>
    </div>
</body>
</html>